भारतीय खगोलभौतिकी संस्थान
Indian Institute of Astrophysics
Exploring the Universe since 1786
An Autonomous Institute under the
Department of Science & Technology
Government of India
Research Highlights
RESEARCH HIGHLIGHTS | IIA
Magnetic topology of quiet-Sun Ellerman bombs and associated ultraviolet brightenings
JAYANT JOSHI | Jan 20, 2025
Context. Quiet-Sun Ellerman bombs (QSEBs) are small-scale magnetic reconnection events in the lower atmosphere of the quiet Sun. Recent work has shown that a small percentage of them can occur co-spatially and co-temporally with ultraviolet (UV) brightenings in the transition region.
Aims. We aim to understand how the magnetic topologies associated with closely occurring QSEBs and UV brightenings can facilitate energy transport and connect these events.
Methods. We used high-resolution Hβ observations from the Swedish 1-m Solar Telescope (SST) and detected QSEBs using k-means clustering. We obtained the magnetic field topology from potential field extrapolations using spectro-polarimetric data in the photospheric Fe I 6173 Å line. To detect UV brightenings, we used coordinated and co-aligned data from the Interface Region Imaging Spectrograph (IRIS) and imposed a threshold of 5σ above the median background on the (IRIS) 1400 Å slit-jaw image channel.
Results. We identify four distinct magnetic configurations that associate QSEBs with UV brightenings, including a simple dipole configuration and more complex fan-spine topologies with a 3D magnetic null point. In the fan-spine topology, the UV brightenings occur near the 3D null point, while QSEBs can be found close to the footpoints of the outer spine, the inner spine, and the fan surface. The height of the 3D null varies between 0.2 Mm and 2.6 Mm, depending on the magnetic field strength in the region. Some QSEBs and UV brightenings, though occurring close to each other, are not topologically connected with the same reconnection process. The energy released during QSEBs falls in the range 1023–1024 ergs.
Conclusions. This study shows that magnetic connectivity and topological features, such as 3D null points, are crucial in linking QSEBs in the lower atmosphere with UV brightenings in the transition region.
RESEARCH HIGHLIGHTS | IIA
Constraining the nature and long-term stability of FRB 20121102A’s persistent radio source
ARVIND BALASUBRAMANIAN | Aug 01, 2025
The persistent radio source (PRS) associated with FRB 20121102A, the first precisely localized repeating fast radio burst (FRB), provides key constraints on both its local environment and the nature of the underlying FRB engine. We present a seven-year (2016–2023) temporal analysis of the PRS, combining new uGMRT observations with archival data across L-band frequencies. We find no statistically significant long-term trend in its L-band flux density. The observed variability is consistent with refractive interstellar scintillation, and the data do not require the PRS to be a source exhibiting strong intrinsic variability. This stability challenges models predicting rapid fading from evolving magnetized outflows, such as those powered by young magnetars or relativistic shocks. Our low-frequency observations show no evidence for spectral evolution between 1.4 GHz and 745 MHz, with a measured spectral index of α = −0.15 ± 0.08, in agreement with values reported from earlier observations in 2016–2017. The PRS remains compact, exhibits a flat radio spectrum, and—if powered by an intermediate-mass black hole accreting at a low Eddington ratio—its radio and X-ray properties are broadly consistent with the fundamental plane of radio-loud AGNs. While not conclusive, this scenario represents a viable alternative to magnetar wind nebula models and warrants further investigation. Furthermore, we find no statistically significant correlation between FRB burst activity and the luminosity of associated PRSs among repeating sources. This apparent decoupling challenges simple progenitor models that directly link bursts and persistent emission. Together, these results suggest that the FRB engine and PRS may in some systems originate from physically distinct sources, underscoring the need for flexible models to explain the diverse environments of repeating FRBs.
RESEARCH HIGHLIGHTS | IIA
Star formation in neutral hydrogen gas reservoirs at cosmic noon
RAVI JOSHI | Dec 06, 2024
We aim to constrain the average star formation associated with neutral hydrogen gas reservoirs at cosmic noon. We used a unprecedented sample of 1716 high-column-density, damped Ly-α absorbers (DLAs) from the Sloan Digital Sky Survey with log(N(H I)/cm‑2) ≥ 21. This allowed us to generate the average Ly-α emission spectrum associated to DLAs, free from any emission coming from the background quasar. We measured the Lyα emission at > 5.8σ level with a luminosity of 8.95 ± 1.54 × 1040 erg s‑1 (corresponding to about 0.02 L⋆ at z ∼ 2 ‑ 3) in systems with average log(N(H I) /cm‑2) of ≈21.2 and at a median redshift of z ∼ 2.64. The peak of the Lyα emission is apparently redshifted by ∼300 km s‑1 relative to the absorption redshift, which appears to be due to suppression of blue Ly-α photons by radiative transfer through expanding gas. We infer that DLAs form stars with an average rate of (0.08 ± 0.01)/fescM⊙ yr‑1; namely, ≈ (0.54 ± 0.09) M⊙ yr‑1 for a typical escape fraction (fesc = 0.15) of Lyman-α emitting galaxies. DLA galaxies follow the main sequence of star-forming galaxies at high redshift, suggesting that the DLA population is dominated by the lower mass end of Lyman-α emitting galaxies.
Press Releases
PRESS RELEASES | SCOPE
Astronomers unveil observational evidence of how cosmic dust grains line up with the Galaxy’s magnetic field
SCOPE | Sep 03, 2025
Scientists have long believed that just like dust particles dancing in a ray of light, tiny cosmic particles floating between stars in the Milky Way act as storytellers of the universe. Now a team of astronomers, has just uncovered the strongest observational evidence yet of how these interstellar dust grains align themselves with magnetic fields in our Galaxy.
This is based on the paper titled "B-fields and Dust in Interstellar Filaments Using Dust Polarization (BALLAD-POL). III. Grain Alignment and Disruption Mechanisms in G34.43+0.24 Using Polarization Observations from JCMT/POL-2", by Saikhom Pravash, Archana Soam, Pham Ngoc Diep, Thiem Hoang, Nguyen Bich Ngoc, and Le Ngoc Tram, The Astrophysical Journal, 2025, 981, 128.
Press release by DST published here.
Press release by PIB published here.
Download the paper here.
PRESS RELEASES | SCOPE
Hanle Dark Sky Reserve star party brings together astronomy enthusiasts for the third year
SCOPE | Sep 26, 2025
Astronomy enthusiasts from across the country participated in amateur astronomy and astrophotography related activities at the third edition of the HDSR Star Party that was jointly organised by the Indian Institute of Astrophysics (IIA), Department of Wildlife Protection of UT Ladakh, and Bhabha Atomic Research Centre (BARC) between 18 and 23 September.
The PIB press release is here.
The DST press release is here.
PRESS RELEASES | SCOPE
Black holes and cosmic jets join forces to shape galaxies
SCOPE | Oct 21, 2025
Black hole activities suppress the birth of new stars around it, shows a new study that can help in a deeper understanding of how galaxies evolve and may provide answers to why some have very low star-formation rates.
This study was published in the Astrophysical Journal, titled “Warm Ionized Gas Outflows in Active Galactic Nuclei: What Causes Them?”, and is authored by Payel Nandi and C.S. Stalin from IIA and D.J. Saikia from IUCAA.
The PIB press release is here.
The DST press release is here.
The paper can be downloaded from here.
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IIA offers a vigorous programme of graduate studies that forms a vital component of research & training. The programme is overseen by the board of graduate studies. The Institute is also a major partner in the Joint Astronomy Programme (JAP), organized by the Indian Institute of Science.
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Solar Studies
Studies of the Sun and solar system have been the longest pursued discipline at IIA. Members of the group conduct theoretical, numerical modeling, and observational studies in solar physics.
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Research interests of the group members range from exoplanets, star formation, stellar evolution, end states of stars, Interstellar medium, the milky way Galaxy, nearby galaxies, active galaxies and time domain astronomy.
Theory
Members of the theoretical Astrophysics group work on a broad range of topics such as black hole astrophysics, pulsars, exoplanets, astrophysical turbulence & magnetic fields, MHD, cosmology and early universe.
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